1. Field of the Invention
The invention relates to a catoptric optical element for generating uniform illuminance distribution by converging light emanated from a light source and, in particular, relates to a catoptric optical element suitable for use in a projection exposure apparatus for manufacturing, for example, a semiconductor integrated circuit having a fine pattern.
2. Description of Related Art
With the improvement of the density and the degree of integration of semiconductor devices such as LSI, IC, and the like, a resolving power required of a projection exposure apparatus that manufactures semiconductor devices such as LSI or IC has been increasing year after year. The resolving power of a projection exposure apparatus is proportional to a numerical aperture on a wafer side of a projection optical system of the projection exposure apparatus and is inversely proportional to a wavelength of the exposure light. Thus, in the field of semiconductor manufacturing, efforts are being made to employ an exposure light having shorter wavelength in order to fabricate ultra-fine IC circuits. The wavelength of the exposure light that is being used is shifting from i-line having a wavelength of 365 nm of a mercury lamp to KrF excimer laser light source having a wavelength of 248 nm. Moreover, ArF excimer laser sources having a wavelength of 193 nm have come to the stage of practical application and, furthermore, efforts are being made to use F2 excimer laser sources having a wavelength of 157 nm.
However, when the wavelength of the exposure light becomes short, the transmittance of material that can be used as a dioptric element is greatly reduced. Thus, it is difficult to design an optical system using a dioptric element for use with light sources in the short wavelength region.
Therefore, a catoptric system that does not include a dioptric system has been proposed for use in manufacturing LSI, IC, or the like, with a projection exposure apparatus. Various types of catoptric systems have been proposed for use as a projection optical system in a projection exposure apparatus for projecting and transferring a circuit pattern formed on a reticle (mask) onto a wafer (substrate).
However, in a projection exposure apparatus using a wavelength shorter than 157 nm, when an illumination optical system for illuminating a reticle plane with uniform illuminance is intended to be constructed, it has been impossible to obtain a uniform illumination light because a fly-eye lens, a rod type optical integrator, or the like, which is a conventional optical system used for reducing non-uniformity in illumination, cannot be used.
The invention is made in view of the aforementioned problem and has as one object to provide a catoptric element capable of producing a uniform illuminance distribution having a wavelength shorter than 157 nm. It also is an object to employ such a catoptric element in an illumination optical system, a projection exposure apparatus, and in a method for manufacturing devices such as, for example, LSI, IC, or other micro-devices (e.g., an imaging element (e.g., a CCD), a thin film magnetic head, and a liquid crystal display element).
In order to address the aforementioned problem, one aspect of the invention provides an optical element made from a hollow member having inner surfaces that can reflect light having a wavelength shorter than 157 nm.
Preferably, the inner reflective surface is coated with a single- or multiple-layer film of coating materials to enhance reflectance. It is preferable that the materials are Mo (molybdenum)/Si (silicon), W (tungsten)/Si, Cr (chromium)/C (carbon), Ni (nickel)/C, NiCr (nickel.chromium)/C, or the like. Accordingly, even an EUV light (an extreme ultraviolet light having a wavelength shorter than 100 nm) can be effectively used with high reflectance.
Another aspect of the invention provides an illumination optical system for illuminating a plane to be illuminated (an illumination plane). The illumination optical system includes a light source for providing a light flux, the aforementioned catoptric element for generating a plurality of images of the light source by internally reflecting the light flux supplied from the light source, and a relay optical system for leading the light from the catoptric element to the illumination plane.
Another aspect of the invention provides a projection exposure apparatus for projecting and transferring a pattern formed on a projection original (e.g., a mask) onto a substrate to be exposed. The projection exposure apparatus includes the aforementioned illumination optical system which forms the aforementioned illumination plane to be illuminated onto the aforementioned projection original.
Another aspect of the invention provides a method for manufacturing a device including the steps of: applying a photosensitive material onto a substrate to be exposed, projecting the pattern formed on the projection original onto the substrate via the projection optical system, developing the photosensitive material on the substrate, and forming a predetermined circuit pattern on the substrate by using the photosensitive material after being developed as a mask.
Furthermore, in the invention, it is preferable that the wavelength of the light to be used is shorter than 50 nm.